The present invention relates to sulfur foams.
A recent patent issued to Dale and Ludwig, U.S. Pat. No. 3,337,355, discloses the production of a sulfur foam using the following steps:
(a) heating sulfur to above its melting point; PA1 (b) blending a stabilizing agent with the molten sulfur; PA1 (c) blending a viscosity increaser with the molten sulfur, steps (b) and (c) being taken in either order with respect to the other; PA1 (d) forming bubbles in the molten sulfur; and PA1 (e) cooling the molten sulfur to below its melting point.
Stabilizing agents disclosed include talcs, mica and plate-like particles. Viscosity increases disclosed include phosphorus sulfide, styrene monomers and polysulfide liquids. According to U.S. Pat. No. 3,337,355:
"The forming of bubbles in the molten sulphur may be done in any conventional manner for forming foams generally such as those methods used in forming plastic foams. These include (1) mechanically mixing a gas such as air with the molten sulphur, (2) adding a blowing agent, and (3) mixing a liquid with the molten sulphur while maintaining a predetermined pressure on the sulphur and then releasing the pressure on the sulphur sufficiently that the liquid will vaporize at the temperature and lower pressure involved. All of these methods must use material free from substance having a deleterious effect upon the process. For example, most members of the halogen family will decrease the viscosity of the sulphur sufficiently that proper foams will not be formed. Examples of blowing agents that are satisfactory are a combination of sodium carbonate or bicarbonate and acid, N,N'-dimethyl N,N'-dinitrosoterephthalamide sold under the trade name Nitrosan, sodium bicarbonate dispersed in a neutral oil sold under the trade name Unicel S, and N,N'-dinitrosopentamethylenetetramine sold under the trade name Unicel ND. Nitrosan, Unicel S, and Unicel ND are products of E. I. du Pont de Nemours & Co."
According to the examples in U.S. Pat. No. 3,337,355, typical ingredients for the sulfur foam include sulfur, talc, P.sub.2 S.sub.5, calcium carbonate and phosphoric acid.
As described in a report by Dale and Ludwig, in foams which they made using phosphoric acid which might or might not contain calcium carbonate their "investigation showed that it was the H.sub.3 PO.sub.4 reacting with the P.sub.2 S.sub.5 that was producing the gases that acted as the blowing agent." See "Investigation of Light Weight Sulfur Foam for Use in Field Applications", John M. Dale and Allen C. Ludwig, October 1969, Cold Regions Research and Engineering Laboratory, Hanover, N.H., particularly pages 3 and 4. The reaction of P.sub.2 S.sub.5 with H.sub.3 PO.sub.4 yields a hydrogen sulfide blown foam.
Production of CO.sub.2 blown sulfur foams using an organic acid and a polyisocyanate is disclosed in Gar Lok Woo U.S. Pat. Nos. 3,887,504 and 3,892,686.